Comments on: Teeny-Weenie Massive Galaxies

By: KS

KS — Tue, 29 Jul 2008 18:35:43 +0000

Very nice post – I stumbled upon this blog by accident but will surely read it regularly. There is another paper on astro-ph by Buitrago, Trujillo and Conselice claiming similar things – they claim two orders of magnitude evolution in the mass surface density. Anyways – we discussed it at our astro-ph group yesterday and no one believed it. The mass is likely incorrect – they claim they use the MAraston models but theu don’t use the existing IRAC data (rest-frame near-IR) where the BC03 and Maraston models actually differ. I also think their measurements of sizes is incorrect. Mancini, working with Cimatti, in Italy is finding that the sizes are grossly underestimated in these analysis.

Anyways – while the interpretationis interesting, I think these papers are wrong. They are not doing a careful job with the analysis which is leading the field astray – well may be not astray but it would be nice to see better analysis of these data which will put this “exciting” discovery to rest

By: Julianne

Julianne — Fri, 09 May 2008 15:31:29 +0000

The odds that Halton Arp is correct on this point are about the same as the LHC destroying the world.

By: Superstring

Superstring — Fri, 09 May 2008 15:06:40 +0000

If Halton Arp is correct, these are not at cosmic distances, They are nearby compact young galaxies.

By: Brian

Brian — Mon, 05 May 2008 12:47:01 +0000

Great post, Julianne. Thanx. A determined sleuth might look for slightly more evolved versions of such galaxies at 9, 8, and 7 Gyr.

By: Ben

Ben — Sun, 04 May 2008 18:45:02 +0000

Neutrinos: Just before a core-collapse supernova occurs, the precursor’s core becomes too massive for electron degeneracy to support it, and electrons and protons combine to form neutrons and neutrinos. The neutron core also liberates its thermal energy in neutrino-antineutrino radiation. Even though neutrinos have a very small cross-section, the interior of the precursor is so dense and hot that this blast of neutrinos starts to blow away the star – the neutrinos are actually the driving force of the supernova. I recall vaguely that without capturing some fraction of the neutrino luminosity, simulations of SNe just can’t get the explosion to explode; the energetics don’t work.

Tiny massive galaxies: It seems a problem if these things are actually that massive. However, even without that high-profile result, if you crank down the mass and accept all their other characteristics, if they are truly quiescent, they are somewhat surprising as very small-radius objects in which star formation has quenched very early. I’ll claim (although I’m open to correction) that there are few or no obvious direct descendants of such objects in the local universe either (there are lots of small galaxies like dwarf ellipticals, but I don’t believe those are old enough). So you would have to merge them away or subsequently add stars around them (to make them cores of bigger old galaxies, or bulges). Or they’re not really quiescent. All of those are possible, it remains to be seen which, if any, are believable.

By: Kea

Kea — Sun, 04 May 2008 07:50:11 +0000

Pitkanen wrote a post on this article already. Maybe there is no mistake.

By: Professor R

Professor R — Sat, 03 May 2008 12:27:26 +0000

This was a superb post, drawing attention to a paper I was completely unaware of, and discussing it at a level some of us can really learn from…
Why can’t there be more posts (and blogs) like this one? Cormac

By: Lab Lemming

Lab Lemming — Sat, 03 May 2008 07:10:50 +0000

Wow, this is great- I could read it all afternoon.

specifically, I had no idea that C/O ratios changed so much as starts evolved- I thought they were either C stars or O stars as a result of initial composition. Very cool.

Just one more totally unrelated question:
I was reading (and blogging about) a geochemistry paper that used isotopic constraints to suggest that the solar system-generating supernova was a Type II with a neutrino-driven wind.

What is a neutrino-driven wind, and how can particles that pass through everything drive?

By: Fermi-Walker Public Transport

Fermi-Walker Public Transport — Sat, 03 May 2008 06:54:41 +0000

Juliane,

Very interesting. Regarding M/L, wouldn’t stellar metallicity be a factor ? That is
since these stars are on the whole more likely to be metal deficient then their present day counteraprts, then I would think that this could affect the stellar luminosity and give a different M/L then if we assumed a solar-type metallicity.
If I recall correctly, metal deficiency tend to make a star bluer and brighter.

By: Julianne

Julianne — Sat, 03 May 2008 03:31:23 +0000

LL — There is a lot of s-process production that goes on in AGB stars. They tend to be pulsators as well, and drive stellar winds, so a fair bit of the freshly produced elements can make their way out. A link to start with might be here.

So, some, but not all, RGB stars will become AGB stars. The inert core doesn’t have sufficient pressure support to hold it up against gravity, so it collapses continuously, becoming denser and hotter as it does so. In higher mass stars, the density and temperature get hot enough that the Helium can start fusing into Carbon. In lower mass stars, the collapsing core never quite makes it, and fusion in the core is over.